A prophy handpiece equipped with a prophy head is for use in removing dental plaque, dental calculus, dental stains, and the like, settled on dental surfaces and interdental spaces, or in polishing dental surfaces after removal of dental calculus and the like by a scaler, or after patch-up of the dental surfaces or the like with a photo-polymerized resin.
FIG. 5 is a cross sectional view showing the construction of a conventional prophy head 50, which is coupled to a sheath, not shown, having a motor accommodated therein. A housing section 51 of the prophy head 50 is formed of a head portion 51a and a mouthpiece 51b, and having a shaft (screw shaft) 52 therein. When it is used, a polishing brush 1 like one shown in FIG. 1 is attached to the shaft 52. In the thus formed prophy head 50, a rotary output from the motor accommodated in the sheath is transmitted via driving force transmitting means consisting of a driving shaft 53a, a driving gear 53b, and an output shaft gear 53c, to the shaft 52, and the thus transmitted output rotates the brush 1 with an abrasive applied thereto, to thereby carry out required polishing work. In place of the brush 1, a rubber cup 2 like one shown in FIG. 2 may be used.
When the prophy head is used, contaminants such as tooth debris, blood and/or saliva can easily enter the interior of the head portion 51a through a gap between the shaft 52 and the mouthpiece 51b. In other words, the gap can become a contaminant intrusion port. If the entered contaminants are allowed to accumulate therein, a bearing 54 and the gear 53c can be disadvantageously eroded. To cope with this disadvantage, an O-ring 55 is disposed on the periphery of the shaft in the head in order to close the gap.
However, the O-ring 55 seals the gap in a manner being in contact with the shaft 52, and therefore driving of the shaft 52 can cause heat generation at the O-ring and wear-out of the same. In addition, a portion of the shaft 52 in contact with the O-ring 55 can wear as well. Therefore, the sealing performance of the O-ring can be deteriorated with the lapse of time, and further the durability of the O-ring and the shaft member can be damaged.